As background technology in this technical field, there is JP 2013-143202 A (PTL 1). PTL 1 describes an electronic device including a circuit board on which an electronic component is mounted and a casing accommodating the circuit board, in which the casing has a structure including a connector accommodating space accommodating and fixing a card edge connector connecting a board connection terminal of the circuit board and an external wiring harness and a board accommodating space, and an end portion where a board connection terminal of the circuit board is formed protrudes from the board accommodating space into the connector accommodating space to be inserted into a board insertion space of the card edge connector, so that the connector terminal and the board connection terminal are contact-connected by a spring mechanism of the connector side. There is described a mechanism that does not cause a relative misalignment or the like between the circuit board and the card edge connector even in a case where vibration or an external force acting on the electronic device is applied. With respect to the material of the connector terminal, there is described a case where Ni/Au is plated on phosphor bronze. However, with respect to the material of the board connection terminal, there is no description.
On the other hand, a material of a board connection terminal of a circuit board connected by a card edge connector is disclosed in JP 2006-9126 A (PTL 2). PTL 2 describes an FPC board where a lead-free solder plating layer having a thickness of 0.2 to 2.0 μm is formed in a wiring circuit of a connector fitting portion of the FPC board, a lead-free solder plating layer having a thickness of 2.0 μm or more is formed in a wiring circuit of a component mounting portion of the FPC board in order to prevent deterioration in wettability by the growth of a Cu—Sn intermetallic compound, and heat treatment is performed under a condition that the lead-free solder plating layer is heated at 140 to 180° C. for 1 hour or at a temperature of a solder melting point or more for 0.1 second or more. There is described an effect that, in the connector fitting portion of the FPC board, it is possible to suppress whiskers growing from the portion where the connector terminal is brought into contact.
In addition, a surface treatment plating material of a contact terminal is disclosed in JP 2014-139345 A (PTL 3). PTL 3 describes a structure where a lower layer made of Ni or an Ni alloy is formed on a metal base and an upper layer made of an alloy plating containing Sn are sequentially formed. As an alloy of the upper layer, an alloy configured with Sn or Sn+In and one or two or more types selected from a constituent element group including Ag, Au, Pd, Pt, Ru, Rh, Os, and Ir are described. There is a description in that the thickness of the alloy layer containing Sn is selected in the range of 0.02 to 0.5 μm, and a solution containing P is used for the surface treatment, so that it is possible to suppress occurrence of whiskers, to obtain wettability of solder after high temperature exposure, a low contact resistance, and a low insertion force of the connector.
In addition, JP 2015-45042 A (PTL 4) discloses a structure including a lower layer made of one or two or more types selected from a constituent element group A including Ni, Cr, Mn, Fe, Co, and Cu, an upper layer made of one or two types selected from a constituent element group B including Sn and In and one or two or more types selected from a constituent element group C including Ag, Au, Pd, Pt, Ru, Rh, Os, and Ir and having a thickness of 0.02 μm or more and less than 1.0 μm, and an intermediate layer made of one or two or more types selected from the constituent element group A and one or two types selected from the constituent element group B and having a thickness of 0.01 μm or more and less than 0.4 μm or an intermediate layer made of one or two or more types selected from the constituent element group C and having a thickness of 0.01 μm or more and less than 0.4 μm, in which the lower layer, the intermediate layer, and the upper layer are formed on a base material in this order, and in which a treatment layer including one or more types selected from a group including O, C, S, P, and N is formed on the upper layer. It is described that it is possible to provide a metal material for an electronic component having a low whisker property, a low adhesion abrasion (low insertion/extraction property), a strong durability even under a corrosive environment, and thus, applications to a connector terminal or an FFC or FPC terminal is described.